Electric vehicles include, a rechargeable battery and a motor and travel by supplying electric power from the battery to the motor. Accordingly, several issues that differ from those for vehicles using an existing internal-combustion engine arise.
For example, it is difficult for electric vehicles to have a battery capacity for providing a cruising distance that is substantially the same as that of existing gasoline-fueled vehicles. In addition, if equipment having a large amount of power consumption, such as an air conditioner, is used, the cruising distance is significantly decreased.
Furthermore, if a drive mode that increases the acceleration performance is selected, the cruising distance is significantly decreased due to an increase in power consumption during acceleration. That is, in an electric vehicle, there is a trade-off between a period of time during which various functions of the vehicle are used and the cruising distance. Accordingly, in order for a driver to find an optimal trade-off point, assistance to the driver is needed by providing various types of information to the driver.
As an example of such an assistance system, Japanese Unexamined Patent Application Publication No. 2001-112121 describes a “navigation system for electric vehicles” that assists a driver to travel to a destination. The system includes a display unit that displays a map and a control unit that switches the operation of a drive motor between a normal drive mode and an economy drive mode. The control unit displays information indicating a maximum driving distance of the electric vehicle in accordance with the current battery level over the displayed map. If the distance to a destination selected by the driver is outside the range, information regarding a charging time required to each the destination is displayed. However, if the distance to the destination is within the range, the control unit starts controlling travel in a normal drive mode. In addition, after the travel starts, in order to support a variation in power consumption caused by a drive operation and traffic jam, the control unit determines whether the vehicle is reachable to the destination on the basis of the distance between the current location and the destination as needed. Thereafter, the control unit switches the normal drive mode to an economy drive mode and displays information regarding charging time as needed.
As another example of a driver assistance system, Japanese Unexamined Patent Application Publication No. 2006-115623 describes a “travelable distance estimation system” including electric vehicles and a data center connected to each of the electric vehicles so as to communicate with the electric vehicle and display information regarding a maximum driving distance accurately estimated on the basis of the level of a battery mounted in the electric vehicle. In this system, every time each of the electric vehicles passes over a node, the electric vehicle transmits, to the data center, information including the amount of battery power consumed in a road link along which the vehicle traveled, a link number of the road link, the model and the model year of the vehicle, the driving characteristics of the driver (three-grade evaluation based on a variation of the speed of an accelerator position), and information as to whether an air conditioner is used. At that time, the data center calculates the average battery power consumed in each of the road links for each of combinations of a driving characteristic, a model of vehicle, and use/non-use of air conditioning. Thus, the data center stores the calculated data therein. Thereafter, if one of the electric vehicles transmits information regarding the start point, the transit point, the destination point, and the calculation conditions (the model of the vehicle, use/non-use of air conditioning, and driver characteristics) to the data center, the data center plans an appropriate route from the start point to the destination point and finds the links that constitute the route, the average battery power consumed for each of the links, and the average battery power consumed for a route from the current location to the destination point on the basis of the above-described calculation conditions. Subsequently, the data center transmits the found result to the electric vehicle.
However, it is difficult to ensure that the vehicle responds faithfully to the driver's intent by simply switching between the economy drive mode and the normal drive mode as in the system described in Japanese Unexamined Patent Application Publication No. 2001-112121. That is, if only the amount of charge remaining in the battery (state-of-charge (SOC)) is the first priority, control based on economy driving is sufficient. However, in reality, the driver wants the driver assistance system to provide not only appropriate control of SOC but also overall control including driver comfort and satisfaction in driving and a certain level of interior comfort. In addition, such requirements and the priorities of the requirements may have a variety of patterns in accordance with an amount of spare time that the driver may have before he/she arrives the destination. That is, by using the technique simply focused on whether the vehicle can arrive at the destination as described in Japanese Unexamined Patent Application Publication No-2001-112121, the demand of the driver who wants comfortable driving cannot be satisfied.
In the system described in Japanese Unexamined Patent Application Publication No. 2006-115623, the maximum driving distance can be accurately computed in consideration of the vehicle individual difference and driver's individual difference, such as the battery power consumption trend (the deterioration trend) based on the model year of the vehicle and the driving characteristics of the drivers. However, only the computed maximum driving distance is displayed on the display unit. Detailed information as to how comfortable driving is scheduled is not presented. That is, information regarding how to drive, what onboard equipment is used, and what setting need to be made on the onboard equipment in order to realize comfortable driving is not provided.